This invention relates generally to manually compressible foam dispensers and particularly to dispensers having a foam producing assembly utilizing at least one rigid porous member.
The production of foam from manually compressible, flexible containers containing liquid and air, which are mixed prior to discharge, is well-known. Such foam dispensers provide an alternative to the rigid type of foam producing containers, generally known as Aerosol dispensers, and offer the advantages of low cost as well as being ecologically acceptable. Flexible cntainer foam dispensers of this general type are disclosed in the patents issued to Stossel, U.S. Pat. No. 3,010,613; and A. L. Boehm et al, U.S. Pat. No. 3,422,993. Flexible container dispensers are also disclosed in U.S. Pat. Nos. 3,428,422; 3,709,437, 3,937,364 4,018,364 and 4,022,351 said patents being owned by the present inventor. The latter three references are particularly significant because they do disclose foam dispensers which utilize a rigid porous member in the foam producing process.
In general, it has been found necessary in prior foam dispensers to provide a homogenizing element to intermix the liquids and air. This element has commonly taken the form of a screen of metal, cloth or plastic and serves the purpose of condensing large bubbles or intermixing liquid and air to form fine bubbles, ie foam. Most foam devices which utilize a flexible, deformable container must discharge the foam through a discharge passage of limited cross sectional area and, in practice, a large porosity screen has been used to minimize back pressure caused when the air and liquid is forced through it. Unfortunately, this creates large bubbles, which are undesirable. On the other hand, placing membranes of fine porosity across the discharge passage, while producing superior foam, creates excessive back pressure. This has been the experience with foam dispensers of the type disclosed in U.S. Pat. No. 3,709,437.
One of the problems in producing an acceptable foam in a foam dispenser utilizing a porous member of the type disclosed in U.S. Pat. No. 3,937,364 resides in the fact that the quality of the foam is related to the porosity of the porous member. Although porous members having the necessary small pore structure to produce effective foam are available, reduction of pore size tends to be accompanied by an undesirable increase in the pressure necessary to move the foam through the porous member.
The present invention solves this problem in a manner neither disclosed or suggested in the known prior art.